<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* 后代选择器 */
    div span {
      color: red;
    }
  </style>
</head>

<body>
  <div>
    <span>div → span</span>
    <p><span>div → p → span</span></p>
  </div>
</body>

</html>